Coated abrasive product and method of manufacturing the same



' Patented se e 6.193s

v UNITED STATE s PATENT orrics i v v 2.128.905 v column anaasrva monuc'r m rm'rnon manor Raymond C.

ACTURING m SAME" m... and We 1.. Melton, mg

as Falls, N. Y., assignors. by mesne assignment's, to The Carborundnm Company, Niagara Falls, N. Y., a corporation of Delaware No Drawing. Application February c, 1935,

- SerlalNo.5,l83'

This invention' relates to an improvement in coated abrasive products and methods of manufacturing the same. More particularly the invention'is concerned with a method of making 5 abrasive coated products wherein the abrasive grains are attached to a backing in a layer substantially one grain deep; as typified by'sandpaper, and in which the secondary or sizing coat-. ing' of adhesive is applied in the form oi a powder ture of abrasive coated products wherein a heathardenable resinor varnish is employed as the base or adhesive coating and is also adaptable to use with other types oi adhesives such as glue.

As is cdmmonly known, the manufacture of sandpaper usually involves the application of two coats of adhesive or hinder commonly spoken of 2 as the base or making coat and the sizing coat.

For example, it is the usual practise to first apply a base coating of liquid adhesive such as glue ora liquid synthetic resin to the backing, sprinkle on the abrasive grain, and then add a secondary or sizing coating of liquid adhesive. The sizing coating usually consists of a solution of the ad- 1 hesive used for the base coating thinned with solvent to a lower viscosity than that of the base coating.

A second method of making sandpaper, which isused particularly where line grit abrasive grains are employed. comprises preparlng'a mixture of the grain with the liquid adhesive and then applying the mixture to the backing.

Both these older methods have the disadvantage that the tops or outer surfaces of the abrasive grains are more or less coated with the adhesive so that the coated product presents a somewhat smooth surface rather than the sharp 4o edges of the uncoated grains. Furthermore,

since the sizing coating must be thinner than the base coating, the application ofv a sizing coating in the usual way requires the removal of 'a relatively large amount of solvent. The removal of '45 this excess solvent lengthens. the time required to dry the adhesive and where materials which require a relatively-expensive solvent are used as I in the case of phenolic resins, for example, the recovery oi! the additional solvent requires a large 50 capacity of rather elaborate solvent recovery ap- 'paratus. 'The use in such cases is further in-,

creased by the roportion oi the solvent which is 'inevitably lost in a method 0! thischaracten- Our invention obviates these diillculties and has II the additional advantage that certain embodiinto a rollto conserve space as ,ples are for the purpose of exemplifying the ina (c1. iii-era ments of the invention are adapted to'the process of curing wherein the coated fabric is wound described and claimed in a copending application by Frank J.

- Tone, Serial No. 756,994 illed December 11, 1934. 5

The method of curing abrasive coated webs by winding them into rolls and heating is particulariy valuable where a binder comprising a heathardenable resin is employed because the curing is a time-temperature function which usually rel0 quires that the coated webs be heated for a comparatively long time in order that the temperature may be kept low enough to avoid weakening .the fabric bacmng. Our process is particularly well adapted to this method of curing because it 15 leaves the outer surfaces oi" the coated webs dry and non-adhesive andjhe product can be wound into a roll without causing trouble from the adhesive sticking to the back of the contiguous layer of backing.

While our invention is adapted to a number 01 variations, we will illustrate it with a few specific examples, it being understood that these exam vention and are not limitative.

Example 1 Sized paper of the type commonly employed in the manufacture of sandpaper and designated as 130 pound cylinder stock is coated with, a layer 30 V of a-normally liquid phenolic condensationproduct resin free from solvents by brushing on the -resin. 'A thin coating of 60 grit silicon carbide abrasive grain is .then sprinkled over the resin coating to form a somewhat discontinuous coat- 35 ing of grain'of a character commonly spoken of as an "open coat. Pulverized phenol-iormaldehyde resin in the so-called A stage is then sifted onto the abrasive coated surface, the excess powder being removed by inverting the coated paper. 40

The product may then be cured for 30 minutes at a temperature of 300 F.

. E'zamplez i {I Sized paper is coated-with a layer of varnish 4 comprising an oil-modified phenolic resin cut with toluol in the proportion of 60 parts of the resin to 40 parts of toluol. 60 grit silicon carbide is then sifted onto the varnished paper in excess, the excess removed, and the coated product is 1 then lightly sprayed with iurfural to moisten the;

surfaces of the abrasive grains. A dry powdered A, stage phenolic resin is then sifted onto the coated' surface, the excess removed, and the product heated to remove the solvent iron 56 the base coating and to first fuse and then heat harden the oil modified resin binder and the pow-'- dered sizing coating.

Example 3 tion of the pulverized resin to the liquid resin increases the depth of coating to the degree required to attach the #36 grit without applying an additional sizing coat.

Example 4 an extent sufiicient to cause it to unite with the base coating of adhesive. dried in the usual way.

As is indicated by the examples, our method is adapted to be used with various types of adhesive materials. It is, for example, well adapted to be used in making coated products wherein the base coating and the sizing coating comprise different materials as illustrated in Examples 3 and 4. It also comprises a number of modifications such as the introduction of the step of moistening the surfaces of the abrasivegrains prior to the addition of the sizing coating, either before or after the grains are applied to the backing.

As illustrated in Example 4, we also contemplate the addition of a material which is a solvent for the dry adhesive used as a sizing material after the sizing coating has been applied. This addition may be water, where glue is the sizing material, or it may be either a volatile or a reac tive type of solvent such as furfural where a synthetic resin such as a phenolic condensation product is used as sizing material. This embodiment of the invention is adapted to be used where the coated product is to be roll-cured, for example, as it provides a'method of thickening or setting up the adhesives to anextent suflicient to permit rolling the coated web without displacement of the coating on the web or adhesion of the The product is then coating to the back of the adjoining layer of coated web.

Although our method is adapted to use with various types of backing material, in general we prefer toemploy a backing which does not absorb the base coating of adhesive as we have found that if absorption occurs the surface of the backing is robbed of some of the adhesive, thereby reducing the effectiveness of the base coating, and at the same time fabric backingsare weakened and embrittled by the impregnating adhesive. Suitable non-absorptive backings are sized papers, metal sheets and the like. We have also found that absorption of resin adhesives can be substantially prevented by preliminarily coating fabrics such as paper or cloth with a thin coating of glue.

Numerous other modifications can-be made in carrying out our invention as, for example, preliminarily heating or drying the coated product before applying the sizing coat or heating the grains to improve penetration of the base coating by the grains, without exceeding the bounds of our invention, the scope of which is defined by the appended claims.

We claim: h

.1 The, method of making coated abrasive products which comprises applying to a backing a base coating of liquid adhesive, adding a thin layer of abrasive grains to the adhesive coated surface, and applying a sizing coating of dry powdered adhesive material, whereby the time necessary for drying the coated abrasive product is reduced and a substantial portion of the abrasive grains thereon remain with exposed edges.

2. The method of making coated abrasive products which comprises applying to a backing a base coating of a liquid comprising a normally liquid resin, adding a thin layer of abrasive grains to the adhesive coated surface, and applying a sizing coating of dry powdered adhesive material, whereby the time necessary for drying the coated abrasive product is reduced and a substantial portion of the abrasive grains thereon remain with exposed edges.

3. The method of making coated abrasive products which comprises applying to a backing a base coating of an oil base varnish, adding a thin layer of abrasive grains to the adhesive coated surface, and applying a sizing coating of dry powdered adhesive material, whereby the time necessary for drying the coated abrasive product is reduced and a substantial portion of the abrasive grains thereon remain with exposed edges.

4. The method of making coated abrasive products which comprises applying to a backing a base coating of a solution of adhesive in a volatile solvent, adding a thin layer of abrasive grains to the adhesive coated surface, and applying a sizing coating of dry powered adhesive material, whereby the time necessary for drying the coated abrasive product is reduced and a substantial portionof the abrasive grains thereon remain with exposed edges. 1 1

5. The method of making coatedabrasive products which comprises coating a surface of a backing with a liquid adhesive, applying a thin layer of abrasive grains to the adhesive coated backing, moistening the'exposed surfaces of the abrasive grains with a solvent for a dry powdered adhesive to be subsequently applied, and dusting on a sizing coating comprising a dry powdered adhesive material, whereby the time necessary for drying the coated abrasive product is reduced and a substantial portion of the abrasive grains thereon remain with exposed edges.

6; The method of making abrasive coated products which comprises attaching a thin layer of abrasive grains to a backing by a base coating of liquid adhesive, applying a sizing coating of dry powered adhesive material and treating the coated product to cause the dry powdered sizing coating to become attached to the abrasive grains and to unite with the base coating of liquid adhesive.

75' The method of making abrasive coated products which comprises attaching abrasive grains to a backing by a base coating of liquid adhesive, applying a sizing coating of dry powdered adhesive material, and heating the coated product to cause the dry powdered sizing coating to become attached to the abrasive grains and to unite with the base coating of liquid adhesive.

8. The method of making abrasive coated prod ucts which comprises attaching a thin layer of abrasive grains to a backing by a base coating of liquid adhesive, applying a sizing coating of dry powdered adhesive material and moistening the coated product with a liquid which is a solvent for the sizing material to cause the dry powdered sizing coating to become attached to the abrasive grains and to unite with the base coating of liquid adhesive.

9. The method of making abrasive coated products which comprises attaching a thin layer of abrasive grains to a backing by a base coating oi? liquid adhesive, applying a sizing coating of dry 

